All Apple iPad USB power adapters are designed for use with power sources rated to provide 100V AC to 240V AC at 50Hz to 60Hz. Apple iPad USB power adapters also comply with the IEC/UL 60950-1 and IEC/UL 62368-1 standards for use with power sources rated to provide 115V AC at 400Hz (typically found onboard commercial airlines).
While your Power Adapter will be fully usable when travelling internationally, you may require a simple pin-adapter to allow the Power Adapter to be used with AC power outlets in different countries. By example, a US flat 2-pin connector will require an adapter for the standard European round 2-pin socket - or UK 3-pin square socket. Travel adapters are readily available at Airports and many electrical retailers.
Be aware that Apple's Travel Kit is limited in that the adapters are only useable with Apple's Power Adapters that have interchangeable duck-heads - whereas regular pin-adapters are both cheaper and potentially useful with many more items that you may be carrying on your travels.